Quadrajet rebuild

[Gregsenne]

It's a M4MC quadrajet. I rebuilt everything on it, but now I'm having trouble getting the stuff on the choke side back together. It's electric choke.

The tang that hits the lever for secondary lockout, I see nothing that will move this tang.

I'm not sure if my fast idle stuff is working right, when I put the fast idle follower on the high step, it doesn't really hold the throttle open like I figured it would.

And my vaccum break that goes to (i guess) the choke flaps on the secondary, pushing it in and out does not move those top flaps on the secondary. Nothing will get them to move (besides moving them by hand). There is no rear vaccum break.

Anyone have any pictures? I have the shop manual for the truck, but those black and white hand drawn pictures are hard to tell, and I can't get a good enough angle on any picture I took, or any pic I found online.

Thanks.

[lurch115]

i have a shop manual in .pdf form but it's to big for me to post it on here for ya. google it and you should be able to find it.

[rcbildr]

Originally Posted by Gregsenne

It's a M4MC quadrajet. I rebuilt everything on it, but now I'm having trouble getting the stuff on the choke side back together. It's electric choke.

The tang that hits the lever for secondary lockout, I see nothing that will move this tang.

I'm not sure if my fast idle stuff is working right, when I put the fast idle follower on the high step, it doesn't really hold the throttle open like I figured it would.

And my vaccum break that goes to (i guess) the choke flaps on the secondary, pushing it in and out does not move those top flaps on the secondary. Nothing will get them to move (besides moving them by hand). There is no rear vaccum break.

Anyone have any pictures? I have the shop manual for the truck, but those black and white hand drawn pictures are hard to tell, and I can't get a good enough angle on any picture I took, or any pic I found online.

Thanks.

Somebody correct me if I'm wrong, but IIRC the vacuum break holds the choke open a little once the engine is running. Right before start up the choke is completely closed and then once the engine is idling the vacuum break holds it open a little bit until the engine is warmed up. The vacuum break also keeps the secondary air valve closed until vacuum drops far enough for it to allow the air valve to open.

[lurch115]

Originally Posted by rcbildr

Somebody correct me if I'm wrong, but IIRC the vacuum break holds the choke open a little once the engine is running. Right before start up the choke is completely closed and then once the engine is idling the vacuum break holds it open a little bit until the engine is warmed up. The vacuum break also keeps the secondary air valve closed until vacuum drops far enough for it to allow the air valve to open.

that is exactly right.

[Gregsenne]

Originally Posted by rcbildr

Somebody correct me if I'm wrong, but IIRC the vacuum break holds the choke open a little once the engine is running. Right before start up the choke is completely closed and then once the engine is idling the vacuum break holds it open a little bit until the engine is warmed up. The vacuum break also keeps the secondary air valve closed until vacuum drops far enough for it to allow the air valve to open.

That's what I thought happened, but if I push the lever on the vaccum break into itself, it still doesn't move the secondary air valve, at all. I'll try to post a picture a little later. The rod that runs from the air valve to the vaccum break simply slides along a slotted groove on the air valve, but it doesn't actually open or close it.

I got the other issues figured out (such as the lever that hits the secondary lockout and the fast idle stuff). It took taking it apart and reassembling it about 3 times, and I'm not sure what I did the last time, but after it all went together, it all worked and made sense.

[lurch115]

okay...sorry i misunderstood you. the only thing the "choke pull off" does as far as your secondary choke butterflies are concerned is that it either holds them shut until vacuum pressure drops in the diaphragm (ie. heavier acceleration). It also helps pull them shut again after letting off the throttle. it has nothing to do with the opening of the secondary butterflies.

[Gregsenne]

Oh, ok, that makes sense. How do they open, then?

[ray_mcavoy]

Those flaps over the secondaries are the secondary air doors.

The Q-Jet has mechanical secondaries ... when they open, it exposes the underside of those secondary air doors to manifold vacuum, drawing them open. Notice how the shaft that they pivot on is offset towards the front to allow them to be pulled open in that manner. The air doors will only open as far as needed to meet the engine's airflow demands.

The choke pull-off on many Q-Jets also serves as a damper to keep the secondary air doors from opening too quickly (creating a bog). That's why there's linkage connecting them to the choke pull-off.

[Gregsenne]

Ok that makes sense. Thanks for the help!!